Purification of manganese sulphate solutions



Patented Aug. 15, 1939 UNITED STATES PURIFICATION OF MANGANESE SULPHATE SOLUTIONS Stephen m. Shelton, Reno, Nev.

No Drawing. Application November 19, 1937, Serial No. 175,538

This invention relates broadly to electrolytic processes for the extraction of metallic manganese from aqueous solutions and, more particularly, relates to the purification of manganese solutions.

While the invention to be described and claimed may be employed for the purification of manganese solutions in general, it is particularly adapted and intended for the purification of manganese sulphate solutions from which metallic manganese is to be extracted by processes such as that described and claimed in my co-pending application Serial No. 100,131, filed September 10, 1936, now Patent 2,119,560, issued June 7, 1938.

In working with managenese sulphate electrolytes, I have .found that even the most minute quantities of nickel and cobalt in the electrolyte are harmful, having the efiect of retarding the electrolytic deposition and causing the deposition of impure manganese on the cathodes. I have found that the removal of these metals from the electrolyte must be complete in order to avoid their deleterious eil'ects, the last one or two milligrams per liter of these impurities being as harmful to proper deposition and the securing of a pure deposit as larger amounts. laboratory processes for the removal of these impurities have been found to be entirely unsatisfactory in commercial operations, not only from the standpoint of proper electrolytic operation and the securing of pure deposits but also by reason of the high cost of the necessary reagents. For example, in laboratory work, dimethyl glyoxime is regarded as an ideal and accurate precipitant for nickel, but this reagent is entirely unsatisfactory for the removal of nickel from manganese electrolytes. This is due not only to the high cost of this reagent but also, and principally, to the fact that it fails to precipitate the last two milligrams per liter of nickel. Alpha furil dioxime is stated by the literature on the subject to be sensitive to one part of nickel in six million but even this reagent fails to precipitate nickel satisfactorily for producing suitable manganese electrolytes. In addition, it is far too expensive to be of value in commercial electrolytic deposition operations. Other means and reagents suggested by the literature for removing nickel and cobalt from manganese solutions have proved to be of equal lack of efllcacy in purifying electrolytes of the type under consideration.

This invention provides a method for effecting the purification of manganese solutions, particularly those of manganese sulphate, prior to electrolysis thereof, by precipitating from the solution impurities of the group including nickel and cobalt. The process according to the invention is operable to cause the removal of the last traces of these impurities from the manganese solution and to cause their precipitation as a compound which will not redissolve in the solution. Further, the process employs reagents which will not adversely aflect the electrolysis of the solution, either by retarding deposition or by contaminating the deposit.

In the process according to this invention the impurities nickel and cobalt are precipitated from a manganese solution, and particularly from a manganese sulphate solution, by treating the so lution with compounds of the so-called xanthate type. These compounds, as is known, are the disalts of thiocarbonic acid and I have found that while it is probable that all of the xanthate-type compounds are effective to a certain degree in causing the desired removal of nickel and cobalt, certain of these compounds are much more effective than others. In general, the process may be eifectively carried out by treating the manganese solution with a compound of a derivative of thiocarbonic acid which is soluble in the manganese solution being treated. Such compounds have the general formula s-x in which M is either a sulphur or an oxygen atom, depending upon whether the compound is a trithiocarbonate or a di-thiocarbonate, R is either an alkali metal atom or an alkyl radicle, and X is. an alkali metal atom. The tri-thiocarbonates of the type S-Na S-Na are not satisfactory precipitants of nickel, cobalt, copper, etc., from manganese sulphate solutions. However, I have found that compounds of the dithiocarbonate class are accurate and complete precipitants of these impurities from maganese sulphate solutions and are effective in removing the last one or two milligrams per liter of nickel, cobalt, and copper from such electrolytes. The di-thiocarbonates, or xanthates, are formed by simultaneously mixing carbon disulphide with an alkali and an alcohol, in the proper stoichometric proportions. For example, if carbon disulphide, sodium hydroxide and ethyl alcohol are mixed in the proper proportions, sodium ethyl di-thiocarbonate is formed, having the following molecular structure:

o-oaa s-m Ifanamyl alcohol isusedinphceoftheethyl alcohol in the described reaction, an amyl di-thiocarbonate is formed which may have the following molecular structure:

O-GsHu The amyl radical may exist as pentasol, di-ethyl carbinol or other isomer but retains the formula CsHlr for empirical formula purposes. Any of the alcohols whatsoever may be used in the preparation of the xanthate compound, the choice depending largely upon the required properties of the resulting xanthate compound with respect to the solution to be treated. and it is to be understood that'my invention is not limited in any way to any particular alkyl di-thiocarbonate or xanthate compound, but is inclunve of all compounds of this class.

Irrespective of the particular alcohol employed, the alkvl thiocarbonates, or xanthates, are effective precipitants of nickel, cobalt and copper from ma sulphate solutions. I have found, however. that xanthates of the heavier alcohols are most eillcient in effecting this precipitation. For example, in amyl xanthate than ethyl xanthate is required to precipitate the final milligram of' nickel or cobalt from a liter of manganese sulphate.- The arnyl xanthate is more expensive than the ethyl xanthate, however, and I have found that satisfactory results may be obtained by employing a mixture of the two,

IncarryingoimmyprocessIprefer-tousethe alkali xanthates. such as sodium ethyl di-thiocarbonate, sodium amyl di-thiocarbonate, potassium ethyl di-thiocarbonate and potassium amyl di-thiocarbonate. The accumulationv of alkali in the electrolyte has not been folmd to have deleterious effects on the deposition of metal from the solution, and the useoi' the alkali xanthates has the additional advantage of aiding inreducingtheacidityofthesolution. While any other compound of the xanthate type might be employed, it would be of course to use only those which are suiliciently soluble in the manganese solution being treated.

It is preferable to unpioy, in actual commercial operation, mores precipitating reagent than is required by theoretical considerations. The exactamount of excess required appears to be of no importance in effectlng the precipitation. but the purification is facilitated by the use of theexcess. Arelatlvelysmallexcessofxanthate intheelectrolytehunodeleteriouseffectontheelectrolysis of the sohition.

flhefollowingbrocedureanexample ofhow the process according to this invention maybe actuallycarried out. The solution which istobe purifiedmayconstituteaneutralsolution of manganese and ammonium sulphates containingfivemilligrams perliter of nickel and fivemilligramsperliterofcobaltatroomtemperature. This sohrflon may be prepared by leaching ores, roasted crmcentrata or other manganese bearing materials with sulphuric acid or ammonium sulphate solution. To this solution isaddedozgramperliterofpotassiumpentasol xanthateandilzgramperliterofsodiumethyl xanthate. The solution is then stirred slowly or intermittently for about three hours and then filtered. No heating is required and the precipitation may be carried out at room temperature. The filtered solution will contain no measureable quantities of nickel or cobalt and the electrolyte, formerly unsatisfactory for manganese deposition, will now deposit pure metallic manganese at reasonably high current eiliciency. The impurities nickel and cobalt will be precipitated as nickel and cobalt xanthates which are insoluble in manganese sulphate solution or in a solution of manganese and ammonium sulphates. If

desired, proper amounts of an ethyl xanthate or an amyl xanthate may be employed as the precipitating reagent instead of the mixture of these two as in the procedure outlined. The use of one only of these reagents will be effective in removing nickel and cobalt impurities within the limitations set forth herelnbefore.

If desired, nickel and cobalt values maybe recovered from the impurity precipitate by suitable means.

I have found that copper, bismuth, lead, antimony, arsenic, iron and silver may be precipitated with nickel and cobalt by the method and means disclosed in this application. These impurities may be removed by less expensive means, however, and it will usually be found that removal of these impurities by such other suitable means and prior to the precipitation of nickel and cobait will be more economical practise.

While I have described the process according to my invention specifically and in detail, it is to be understood that the invention is limited only by the scope of the appended claims.

What I claim is: I

1. In a process for the electrodeposition ofmetallic manganese from an aqueous manganese sulphate solution, the step of purifying the solu-' tion prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution a xanthate.

2. In a process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution, the step I of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution an alkalimetal xanthate.

3. In a process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution. the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution an ethyl xanthate.

4. In a process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises ad ing to the solution an amyl xanthate.

5. In a process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution, the step of purifying the, solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution an alkyl thiocarbonate compolmd at room temperature.

6. In a process for the electrodeposition of 'metallic manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution an amoimt of an alkyl thlocarbonate compound which is in excess of the amount theoretically required to form di-thiocarbonate compounds with the nickel and cobalt in the solution.

7. In a process for the electrodepositlon of metallic manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution a mixture of alkyl thiocarbonates.

8. In a process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution a mixture of amyl thiocarbonate and ethyl thiocarbonate.

9. In a process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution a mixture of an amyl xanthate and ethyl xanthate.

10. Ina process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution a mixture of an amyl xanthat'eand an ethyl xanthate both of which are appreciably soluble in the solution.

11. In a process for the electrodeposition of metallic manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution a mixture of an alkali metal amyl xanthate and an alkali metal ethyl xanthate.

12. In a process for the electrodeposition of metallic-manganese from an aqueous manganese sulphate solution, the step of purifying the solution prior to electrolysis by removing nickel and cobalt therefrom, which comprises adding to the solution a mixture of an alkali metal amyl xanthate and an alkali metal ethyl xanthate both of which are appreciably soluble in the solution.

STEPHEN M. SHELTON. 

